The present invention relates to a device or unit having a simple structure for easily detecting ultraviolet rays.
One typical example of a conventional device for detecting ultraviolet rays comprises an outer casing having a box shape for shielding external lights from entering the casing, a detector for detecting the ultraviolet rays disposed inside the casing and an ultraviolet ray pass filter disposed inside an entrance window formed to the casing as an opening through which light beams enter the casing. The detector is generally constituted by a photodiode, which is sensitive to other light beams as well as the ultraviolet rays and, accordingly, only the ultraviolet rays can be detected by the cooperation of the photodiode and the ultraviolet ray pass filter.
However, in the conventional ultraviolet ray detecting device having the structure described above, it is necessary to incorporate an electric power source to drive the photodiode and the detector is not operated without using the power source, thus being not simple and not easily operated. In addition, a phoodiode having a large light receiving area is required in accordance with the enlargement of the light entrance window, which is not econimical and is inconvenient.